Systems for thermal development of flexographic printing plates are well known in the prior art. A typical system for thermal development of flexographic printing plates comprises a plate processor that accepts a previously formed and imagewise actinic radiation exposed flexible sheet. The flexible sheet typically has a base layer and one or more adjacent layers of a radiation hardenable elastomer material (curable layer). Optionally, the flexible sheet may comprise an infrared sensitive layer.
U.S. Pat. No. 5,175,072 to Martens, the subject matter of which is herein incorporated by reference in its entirety, describes a method for forming, irradiating, and thermally developing a flexographic sheet to manufacture a flexographic printing plate. Thermal development plate processors are further described in U.S. Pat. No. 5,279,697 to Peterson et al., and in WO 01/18604 to Johnson et al., the subject matter of each of which is herein incorporated by reference in its entirety. The plate processor described by Johnson et al. is similar to the plate processor described by Peterson et al.
Prior to using the plate processor to thermally develop the flexible sheet to form the flexographic printing plate, the flexographic printing plate is subjected to an imaging step. In a typical imaging step, a template or mask is first placed over the radiation curable layer, which is imagewise exposed to actinic radiation to harden (cure or crosslink) a portion of the radiation curable layer. Alternatively, the infrared sensitive layer may be ablated by an infrared laser to create an in situ mask on the radiation curable layer. A portion of the radiation curable layer is then cured by actinic radiation through the lower surface of the base to form a cured “floor.” Next, the radiation curable layer film is imagewise exposed from the opposite surface to cure the desired portions of the plate. The radiation curable layer after curing consists of cured portions and uncured portions. At this point, the flexible sheet may be developed in the thermal plate processor.
The development of the relief structure formed during the imaging step is accomplished by removal of the uncured portions of the radiation curable layer. The radiation curable layer is contacted with a preheated web of absorbent material. The heat in the absorbent web is transferred to the radiation curable layer upon contact, and the temperature of the radiation curable layer is raised to a temperature sufficient to enable the uncured portions of the radiation curable layer to soften or liquefy and be absorbed into the absorbent web. While still in the heated condition, the absorbent sheet material is separated from the cured radiation curable layer in contact with the support layer to reveal the relief structure. After cooling to room temperature, the resulting flexographic printing plate can be mounted on a printing plate cylinder.
Thermal plate processors routinely reach temperatures in excess of 150° C. during removal of uncrosslinked portions of the radiation curable layer. At this temperature, the monomers and polymers that make up the plate can volatilize.
Thus, there is a need in the art for an improved ventilation system for a thermal plate processor that can treat vapors resulting from the removal of uncrosslinked portions of the radiation curable layer of the flexographic printing plate.
The inventors have developed an improved ventilation system that is operably connected to a suitable plate processor and that operates in a “closed loop.” The improved ventilation system of the invention exhausts contaminated air from the plate processor, filters the contaminated air to remove the contaminants, and returns the treated air to the plate processor.